Filar control



June 9, 1925. 1,540,770

- M. B, FIELD FILAR CONTROL Filed Got. 12, 1921 5 Sheets-Sheet 1 QIWMMLN M 65.31 Judd M. B\ FIELD FILAR CONTROL June 9, 1925 s Sheet-Sheet 2 Filed Oct. 1921 lime 1925.

M. B. F ELI5 FILAR CONTROL Filed Oct. 1921 s sheets-sheet s I MW.

Patented June 9, 1925.

MICHAEL :smrrrnnn, or onasoow scornann, AssIGNoaTo KELVIN BO'TTOMLEY s3 BAIRD, LIMITED, or GLASGOW, soornann, A ooaroaa'rrou OFGREATYBRITAIN.

FILAR con'rnon Application. filed October 12,;1921L Serial No. 507,332.

To all whom it mag concern; s

Be itknown that L'MICHAEL BIRT FIELD,

a subject of the King of the United Kingdom of- Great'Britain and Ireland, and residing at Glasgow, Scotland, have invented a certain new and useful Improvement in Filar Controls, of which the following is a.

I specification. V i.

' This invention relates multi-filar suspensions or control means. I

A well-known form of'bifilar suspension comprises two flexible filaments or ligaments assumed for the purpose of explanation. to

' have negligible torsional rigidity, hanging substantially vertically ata distance apart which is small in relation to the length of the 1 filaments,the filaments being attached 7 at the upper end to a frame and supporting the moving system from the lower end. The weight of the moving system constitutes a 9 load on the filaments and produces tension therein. When the only forces acting upon the moving system arethose of gravity and the tensions of the filaments, the two filaments are in a plane, the load beingat its lowest level under these conditions. I shall hereafter refer to this position as the 5 initial position.

. V Asis understood, if an angular displacementabout the vertical axis oft-he system be imparted to the suspended load, the filaments of such a bifilai' suspension twist out of the original plane and the loadis raised, whereby a gravitational turning ,moment is set up, tending to restore the system to the initial position; Thus, when the turning of themoving system or load occurs, the filaments are on a vertical surface which 43' has a twist aboutthe vertical axis.

The turning moment tending to restore thesystem to [theinitial position is termed the control. The amount ofrcontrol depends in part on the manner in which the two filafreely about a horizontal axis, passing to new or improved 10 forms of instruments compris ng b 'filar or ments share the load and may, therefore,be--

through the vertical axis at right angles to the plane containing .the filaments when in' the initial position. y

g If the length of the filaments be great in relation to their separation,as control is proportional to the angle of angular displacementof the load from its initial positiona Thus, the maximum controlfoccurs with an angle of twist of 90, and with increasing angles the contiol decreases. If, therefore, the deflecting force be sufficient to produce a deflection greater than 90, thesystem will. be unstable. The use of suchbifilarsuspensions and conis usual, the; sine of the trol means has heretofore been confined I p to the first quadrantof rotatory motion, and,

in fact, it has'be'en usual to restrict the :mo-

tionto comparatively small angles from'the initial position.

It will further be observed-that if the filaments be parallel in the initial position, when angular displacement occurs, the separation varies from point to point, the fila-,

ments beingnearest together at their cen-- tral points and beingsstraight from end to end. V

So' far as I am "aware, it has not hitherto been proposed to interpose between the ,fila-. ments'distance pieces distributed along their length in the manner which'I shall describe and as the result of which the filaments do notfollow straight line courses fromiend to end when in the twisted position, whereby there s obtained a useful of the law of control.

modification v My invention contemplates new. or; improved forms of bifilar or multi-filar suspensions or control means for instruments wherein the moving system is controlled by such suspensions or control means and where the tension in the filaments controlling, load is independent ofthe weight of the moving system; and means for anchoringthe nonrotating end of the suspension or control means. 1

. The characteristics of the bifilar or multifilar suspensionsor control means contem-' plate-d by this invention arer'filaments under.

tension, directed in general along the axis of turning, attachedvat oneend to a rotatable member and attached at the other end rigidl i or yieldingly to the frame, so that rotation is accompanied by change in the inclination of the filaments to the plane transverse to the axis of rotation, whereby the tension components in such transverse plane give'rise to'a turning moment about said axis varying as the angle of rotation is varied.

' Afeature of my invention consists in disposing'a strut or struts between the filaments at a location or locations between the ends thereof so that as the suspension or control means is twisted, given separation is maintained at such location or locations, and the filaments do not follow straight line courses from end to end. In thisway, the law of control is altered so as to'render th suspension or control means more suitable for various purposes.

In the drawings igs. 1.and 2 are elevations at right angles to one another of a concentric watt-meter for the measurement of large alternating current powers.

Fig; 3 is a perspective view illustrating one form of anchorage for the bifilar suspension.

Fig. 4; is a perspective View showing a modified form of anchorage.

Figs. 5 and 6 are diagrams of movements controlled by filar combinations.

Fig. 7 is a detail view showing a'form of strut interposed between the'filaments of the bifilar suspension. j

Referring to Figs. 1 and 2, 1 denotes the central conductorwhich carries the main current. (The terminal attached to the. conductor is not shown, but may be assumed to be located on the right hand side of the central conductor shown broken oil inFig. 1.) The current passes axially along the central conductor 1 into the flange 2, thence to the flange 2 and cage bars 3 into the flanges 1 and 4; and the neck piece and thence to the second main current terminal, not shown, but also assumed to be'located on the right hand side of the instrument, Fig. 1. i I

The shunt current coils 6 are ar 'anged one above and one below the central conductor 1, being held together on a light insulating frame 7 and supported on a spindle 8 capable of turning about a vertical axis, as hereafter explained. A lower spindle 9 attached to the coils carries a damping vane 10 which rotates in a liquid damping pot 11 carried by the base 12. A three-legged bracket 13 is support-ed on a horizontal plate 14 insulated from the cage by the insulating strips 15 and carries on its upper end a rotatable head for adjusting the in strument to zero, or, in other words, for bringing the pointer to the zero mark of the scale. r

The rotatable head includes a wormwheel 16 threaded on a spindle 17 arranged of the. knife-edge 19 in azimuth.

The general construction of such wattmeters 1s well understood and further explanation of the details heretoforereferred 'to is considered unnecessary.

In the knife-edge bearings 19 is mounted a member 22. which carries an insulating plate 23. To the insulating plate 23 are attached two metallic strips 24 which are connected by fine flexible wires 25 to shunt terminals 26 carried by the bracket 13. The metallic strips 24 form the upper terminals to which a bifilarladder is attached by screws 28. The bifilar ladder consists of two filaments 29 distanced apart by struts 30, the upper and lower ends of the filaments terminating in insulating plates 31 which-support metallic strips 32 to which the ends of the filaments are electrically con nected.

'In the form shown, the path of the cur rent entering the moving system is as fol-- lows I From one of the terminals 26 through one of the connections 25-to a strip 24, thence by a screw 28 into an upper strip 32, thence through one filament to the corresponding lower strip 32 and through the spindle 8 into the coil, returning through a wire' (not shown) wrapped round the spindle 8, to the second terminal 26in a manner similar to the foregoing.

36 (Fig. 1) isa pointer which is attached to a member 38 carried by the spindle 8 and which cooperates with a fixed scale 39 40 is a mirror attached to the moving system for co-operation with a beam of light and a distant indicating scale in well knowr manner.

In order to avoid sharp bending or kinking of the ligament material in the imme diate neighbourhood of the points of attachment to the plates 31 and to the struts 30, when the'suspension is twisted, I find it desirable to constrain the ligaments to bend around or unbend from suitably curved surfaces or members formed on or attached to the struts 30 and plates 31. Sharp bending of the ligaments is undesirable since it may'set up destructive distortion of the material and it may give'rise to a sub-permanent set of the material which militates against precision of measurement. 'In Figs. 1 and 2'," the curved constraining members or surfaces are not shown on ac count of their smallness and the struts shown in these figures are to be considered as indicative of the. principle rather than as illustrating constructional features: 2

1,546,770 I v I V In 7 shown a desirable 'form ot strut cons sting, or a round rod with enlarged cylindrical heads in" the form of 'a dumb-bell. The headsfiare slotted" and the ligament" meeting 'the surface tangentially passes a quarter way round the cylindrical head, back "through the, slot, a further quarter way round in theopposite direction,

and 'leaves tangentially, -.as I indicated.

Fig. 3 illustrates a construction for anchoring the lower end of thebifilar suspen-" sion in such wise that it is free to move over a small range m thevertical d rection but is restrictedfrom rotation about a vertical. axis.

55 denotes the filar pair, 56 a cross strut, and 57 the bottom member which constitutes the load on the filar pair. The

member 57 is anchored, by hinged links 58, 59 and 60, to spring members 61, 62, 63, which are carried on supports 64, on a base plate 66. The member 57 is also an- -chored, by links 67 68, 69 to the bell-crank levers 70, 71 and 72, which are supported pivotally on brackets 73, 74, Thelinks 67, 68, 69 are disposed normally in a horizontal plane and are under tension due to small weights at 75, 76, 77 on thehorizontal arms of the bell-crank levers. The arrangement is such that vertical motion of the member s is permitted while horizontal motion and rotatory motion about a vertical axis are prevented, and the tensions in the links are out the range of twist to which the bifilar suspension is subjected. Screws 78,- 79, 8O serve for centralizing the member 57 in the vertical axis of the instrument. Guard wires 81 serve to limit .the motion of the bell-crank levers during transport vetc. l/Vhen current is led into and out of the moving system by means of the filaments, they are extended below the lower strut and attached with easy bends to terminal posts 82.

Fig. 4 represents another form of anchorage in which the bottom member of the bifilar suspension is a Y-shaped piece 83, anchored by three hinged links 84, 85, 86, of which the links 84: and 85 are attached to spring plates 87, 88 and the link '86 is attached to the depending arm of the bellcrank lever 89. i r

Figs. 5 and 6 represent diagrammatically various arrangements of movements controlled by filar combinations where the control load is independent of the weight of the moving system. Fig. 5 shows. an arrangement where the coil A is supported upon a pivot B, balanced so that itscentre of gravity is at the pivot point, and 'thelowerends of the filaments C are attached to a pivoted or knife-edged strument so as tollie substantially horizon V tally and w produce tension in the filaments, by its own weight inodifiedfas may be dc sired by adjustment of the counterbalance weight W orby additional.weighting] or otherwise. i a Fig; 6 shows a moving system comprising a coil A 1 supported on a single pivot B where the' bifilar combination C is arranged above the coil, the" pull being upwards and effected through the 'medium'ot' an overbalanced drum E supported on a knife-edged bearing F. It will be understood that the axial'tension exerted onthe filaments C is less than the weight of the moving system, so that there is in all'oiris maintained in position. The moving system is so balancedithat the centre ot gravity is at the centre of the coil. In Fig. 6 there is illustrated an intermediate strut whereby the tension in the ligaments is equalized.

By theterm filaments ldintend to inelude not only fine threads but also eX- tremely narrow strips.

Byv the term moving system I intend to imply the rotatable member to which one end of the suspension or control means is attached, together with the relative pointer, balance arms, and other members rigidly attached to said rotatable member.

I claim V r 1. In a measuring or like instrument, in

combination, a uni-pivoted moving system so balanced thatthe centre of gravityof said system is at the pivot point, a filar control means for said system arranged above said system and comprising filamentsconnected at their lower ends to said system and anchored at their upper ends in such wise as to permit axial motion of the upper ends-of said filaments while'restricting rotatory motion, means for spacing said filaments apart intermediate their ends, and means for producing tension in said filaments. g I

-2. In a measuring or like instrument, in combination, a moving system, a filar control'means for said system comprising filaments each connected at one end to said sys tem andanchored at the opposite end, and means independent of said system for pro,- ducing tension in said filaments.

3. In aineasuring or like instrument, in

combination, a movingsy'stem, a filar con exercising axial tension in said filaments.

i 4. In a measuring or like instrument, in combination, a pivoted movlng system, a

bifilar suspension above said system,- andmeans independent of said SYStQDIBXBlClS- ing in said suspension axial force less than the ei ht of said system.

5. In a measuring or like instrument, in combination, a uni-pivoted moving system so balanced that the centre of gravity is at thepirot, filar control means comprising filaments each connected at one end to said system, and means for anchoring each of said filaments at theopposite and in such Wise that the anchored ends ofsaid fila ments are free to move over a. small range in axial direction but arev restricted from rotation. V I

A filar control means for measuring instruments and thelilge comprising a system of filaments in parallel, distance means for spacing said filaments apart intermedi l ate their ends, and means for anchoring each of said filaments fieigibly at one end in such ise as to permit axial motio'n; of the anchored endsof said filaments over the requisite range without sensibly modifying the tension of said filaments butto restrict rotation of the anchored ends of said filaments about the axis of. said-system.

'7. A filar control means ior measuring instruments and the like, comprising fila-' merits in 'pa allel and azstrut connecting said 1filamentsintermediate their ends in 30 such wiseuas to equalize the tensions said filaments. V

8. A filar control means formeasuring instruments and the liketcmhprieing filaments in parallel, attachment members at 35 the ends of; said filaments, and-a distance picceconnecting said filaments intermediate their ends.

'9. In combination, a pivoted moying sys-.. tem, a pivot bearing for said system, filar 40 control means for (said system comprising li 'ainents'connected to said system, and means a; producingtension infthe ligamentswhereby to relieve the pivot bearing of part of the Weight of said system. 45

. Intestimony WhereofI have signed my name to this specification in the presence of two. subscribing itnesses. MICHAEL BIB-T FIELD. lVitnesses i I ISABEL RoLLo,

MAY ROSS. 

